It is already known to carry out corrections of signals distortions, caused by a transmission line, in a data transmission with square wave signals between terminal stations and a master station. The publication, Elektronik, No. 25, 1983, pages 56 to 62, describes an adaptive distortion correction network having a filter characteristic which automatically adapts to the distortions, caused by the transmission line, of heavy harmonic-containing square wave signals. The distortion correction network described therein is formed by an orthogonal filter of relatively elaborate design, the aforementioned filter characteristic being set on the basis of a signal evaluation of the distorted signal, and a control unit connected thereto.
One disadvantage of such a correction network is that control of the input signal level to a defined value is provided only to a limited extent; only short-time fluctuations in the amplitude of the signal are equalized. Secondly, to carry out the control process, the presence of a signal is always necessary and the control process always takes a certain amount of time. Lastly, the correction network does not provide a constant compensation of the signal level attenuation fixed over an extended period of time.
It is therefore an object of the invention to ensure in a simple manner that in a signal transmission over different distances a constant level of the received signal can always be made available for evaluation.